Learn Hardcore Indonesian: Jarak rumahnya ke kampus hanya dua kilometer, jadi dia jalan kaki. - The distance from his/her house to campus is only two kilometers, so he/she walks.

Jarak X ke Y ... = The distance from X to Y …
You can also say Jarak dari X ke Y ..., adding dari (from), which is very common:
- Jarak dari rumahnya ke kampus hanya dua kilometer.

Why is it rumahnya and not rumah dia?

-nya is a possessive suffix meaning his / her / its (or their in some contexts).

rumahnya = his/her house
rumah dia is also grammatical but sounds a bit more casual and less compact.

In writing and in more neutral style, rumahnya is more natural than rumah dia. Both are correct, but -nya is very common and you should get used to using it.

Can -nya here mean the, not his/her?

Sometimes -nya can mean the or give a general/definite meaning, but in this sentence it is most naturally read as his/her.

rumahnya here: context suggests his/her house (we are talking about one specific person: dia).
If we wanted a neutral the house, we would usually just say rumah itu (= that house) instead.

Why is it ke kampus and not di kampus or something else?

ke means to / towards (direction).

ke kampus = to the campus

Compare:

di kampus = at the campus (location, no movement)
dari kampus = from the campus
Here we’re talking about distance between two points, so we say jarak ... ke kampus.

Could I say Jarak dari rumahnya ke kampus instead of Jarak rumahnya ke kampus? Is there a difference?

Yes, you can say both:

Jarak rumahnya ke kampus ...
Jarak dari rumahnya ke kampus ...

Adding dari makes the “from” part explicit but doesn’t change the basic meaning. Both are natural. Jarak dari rumahnya ke kampus might sound slightly more formal or explicit, but the difference is small.

Why is there no word like “is” (like adalah) before hanya dua kilometer?

Indonesian often drops a copula (the verb to be) when linking a noun and a description.
So:

Jarak rumahnya ke kampus hanya dua kilometer.
literally: Distance his/her house to campus only two kilometers.

You could add adalah in more formal writing:

Jarak rumahnya ke kampus adalah dua kilometer.
But in everyday speech, adalah is usually omitted in this kind of sentence.

What does hanya do here, and can I use cuma or saja instead?

hanya means only / just and expresses that the distance is small.

Alternatives:

cuma: more informal, same meaning
- Jarak rumahnya ke kampus cuma dua kilometer.
dua kilometer saja: saja also gives a similar only nuance
- Jarak rumahnya ke kampus dua kilometer saja.

All of these are natural; hanya is neutral and works well in both spoken and written language.

What does jadi mean here, and how is it used?

jadi is a conjunction meaning so / therefore / as a result.
It connects the reason (short distance) with the result (he/she walks):

Jarak rumahnya ke kampus hanya dua kilometer, jadi dia jalan kaki.
= “The distance is only two kilometers, so he/she walks.”

In more formal language you might see oleh karena itu, maka, or sehingga, but jadi is very common and natural in everyday speech.

Why is it jalan kaki and not just jalan or berjalan?

jalan kaki is an idiomatic expression meaning to walk (on foot), specifically as a way of going somewhere.

Compare:

jalan alone can mean road, street, or to walk, but it’s less specific as transportation.
berjalan = to walk / to go / to run (function), more formal or general.

To say someone goes somewhere by walking, jalan kaki is the most natural everyday phrase.

Dia jalan kaki ke kampus. = He/She goes to campus on foot.

Why is it dia jalan kaki and not dia berjalan kaki?

Both are possible:

dia jalan kaki: more informal, common in conversation
dia berjalan kaki: slightly more formal or careful speech

The meaning is basically the same. In everyday spoken Indonesian, people often drop the ber- prefix and just say jalan kaki.

Could I leave out dia in the second clause and just say ..., jadi jalan kaki?

Yes. Indonesian often drops pronouns when the subject is clear from context.

So you can say:

Jarak rumahnya ke kampus hanya dua kilometer, jadi jalan kaki.

This would still be understood as he/she walks (to campus), because the subject was already mentioned. Including dia just makes it slightly clearer or more explicit.

How do we know if this means “he/she usually walks” or “he/she is walking (now)”?

Indonesian doesn’t mark tense the way English does; it relies on context.

The sentence by itself can be understood as:

a habitual action: he/she generally walks to campus
or a more general statement about what he/she does, given the short distance

If you want to make the habitual meaning explicit, you could add a time word:

Setiap hari dia jalan kaki. = He/She walks every day.
For a “right now” sense, you’d normally have more context or add something like sekarang (now).

Is kampus an Indonesian word or a loan word, and is it formal?

kampus is a loan word from English “campus”, but it is fully accepted and standard in Indonesian.
It’s used in both informal and formal contexts to mean the physical university campus area.

Examples:

Dia tinggal dekat kampus. = He/She lives near campus.
Fasilitas di kampus ini sangat lengkap. = The facilities on this campus are very complete.